Low temperature and efficient fractionation of lignocellulosic biomass using recyclable organic solid acids

ABSTRACT

Methods of fractionating lignocellulosic biomass using hydrotropic solid organic acids are provided. Also provided are methods of forming lignin particles, furans, sugars, and/or lignocellulosic micro- and nanofibrils from the liquid and solid fractions produced by fractionation process. The fractionation can be carried out at low temperatures with short reaction times.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 15/882,078 that was filed on Jan. 29, 2018, which claimspriority to U.S. provisional patent application No. 62/452,282 that wasfiled on Jan. 30, 2017, the entire contents of both of which are herebyincorporated herein by reference.

FIELD OF THE INVENTIONS

The inventions described herein relate to the field of fractionation oflignocellulosic plant biomass, such as wood biomass, for value addedutilizations.

BACKGROUND

The per capita demand for cellulosic fibers in textiles is expected toincrease from 3.7 to 5.4 kg in the next 15 years. With the Earth'spopulation estimated to grow from 6.9 to 8.3 billion in the same timeperiod, it is expected that cotton, a major source of cellulosic fibers,will not meet market demand due to the estimated production of only 3.1kg per capita in 2030, based on anticipated shrinkage of cotton growingarea (Hauru et al. 2013). Therefore, producing man-made cellulosic-basedfibers, such as viscose, cellulose acetate, etc., from dissolving pulpwill be a necessary alternative to make up this large market shortage ofat least 1.7 kg per capita for native cellulosic fibers. Dissolving pulpfibers are commercially produced using either sulfite pulping orhot-water pre-hydrolysis coupled with kraft pulping, both developed inthe 1950's. The main problems with sulfite pulping are chemical recoveryand environmental concerns due to SO₂ air emissions. The metal base insulfite pulping, excepting magnesium, cannot be recovered.Pre-hydrolysis with kraft pulping is very expensive in terms of energy.Chemical recovery in kraft pulping is commercially practiced using theTomlinson recovery boiler, but is capital intensive. The hemicellulosicsugars from hot-water pre-hydrolysis are often discarded to save energy,which can create substantial biochemical oxygen demand (BOD) problems.

Cellulose nanomaterials have attracted great attention recently fortheir unique optical and mechanical properties (Moon et al. 2011; Zhu etal. 2016). Most of the published research, however, has been focused oncellulose nanomaterials produced using bleached fibers that do notcontain lignin. Lignin is relatively hydrophobic, which can bebeneficial for certain applications. Unfortunately, only a few studieshave reported the production of lignin containing cellulosenanomaterials from commercial unbleached chemical pulps using directmechanical fibrillation, which is energy intensive and does not producesurface functional groups which aid dispersion (Rojo et al. 2015; Spenceet al. 2010). A study on the production of lignocellulose nanomaterialsdirectly from wood is reported as a patented process by AmericanProcess, Inc. at high temperatures using an organic solvent solution ofconcentrated ethanol and sulfur dioxide (Nelson et al. 2015).

Nano sized particles have attracted great interest due to their largespecific surface areas and shape dependent properties for a variety ofpotential applications (Xia et al. 2009). Organic nanoparticles (Kamalyet al. 2016; Mavila et al. 2016; Reisch and Klymchenko 2016), especiallythose derived from biodegradable and benign natural biopolymers, such ascellulose, chitin and DNA, are more attractive from a sustainabilitypoint of view. Lignin, the second most abundant natural polymer from aplant biomass cell wall, has so far found limited economical utilizationother than as a boiler fuel through combustion in pulp mills (Duval andLawoko 2014; Upton and Kasko 2016). With rapid advances innanotechnology, lignin, as a renewable and abundant biopolymer, hasgained growing interests in the nanotechnology field (Frangville et al.2012; Nair et al. 2014). Lignin nanoparticles (LNPs) have potentialapplications in developing novel and biodegradable materials andadvancing biotechnologies (Jiang et al. 2013; Qian et al. 2014; Richteret al. 2015; Ten et al. 2014).

The commercial applications of LNPs through industrial processing,however, are impeded by the difficulties in economical production fromthe plant cell wall. Almost all of the existing methods for theproduction of LNPs use commercial technical lignin which requiresdissolution in solvents, such as ethylene glycol, acetone,tetrahydrofuran (THF), or N,N-dimethylformamide (DMF), followed byeither acidic precipitation (Frangville et al. 2012; Richter et al.2016), hexane precipitation (Qian et al. 2014), dialysis (Lievonen etal. 2016), or atomization and drying (Ago et al. 2016). The use oforganic solvents such as ethylene glycol and THF is an environmentalconcern and increases LNP cost for solvent recovery. Also, the LNPproperties are affected by the original feed lignin sources generatedfrom various pulping processes.

Hydrotropic chemistry using concentrated aromatic salts as solvents forsolubilizing a range of hydrophobic compounds was discovered in 1916 byNeuberg. Its application for fractionation of lignocellulosic biomasswas first practiced by McKee (McKee 1943). For pulping poplar using30-40 weight percent (wt %) aqueous sodium xylenesulfonate liquor, areaction of temperature of 150° C. for 11-12 hr was needed to obtain acellulosic solids yield of 52% (McKee 1946). There are many hydrotropicagents that can be used to dissolve lignin (Procter 1971). The most usedsalts were sodium salicylate and xylenesulfonate, cumenesulfonate.Sodium xylenesulfonate was found to have very strong hydrotropicactivity at 30 wt % and only required a 3-time dilution to lose itshydrotropic properties and, thus, precipitate lignin (Robert 1955).There have been numerous studies on hydrotropic pulping since itsinvention (Gromov and Odincov 1959; McKee 1954; Procter 1971) includingusing additives (Kalninsh et al. 1967; Nelson 1978). However, theprocesses were never commercialized due to low pulp yields, poor pulpmechanical properties, and very long cooking times. Moreover, theprocesses were not suitable for pulping softwoods, due to insufficientdelignification (Procter 1971). Recently, hydrotropic pulp was found tobe enzymatically digestible for sugar production (Korpinen and Fardim2009). To reduce reaction time, additives such as formic acid andhydrogen peroxide were used (Gabov et al. 2013). A recent study includedthe characterization of lignin from modified hydrotropic processes usedfor subsequent sugar production (Gabov et al. 2014). The utilization ofhydrotropic lignin, however, has remained limited (Kalninsh et al. 1962;Procter 1971).

SUMMARY

Methods of treating lignocellulosic biomass to fractionate thelignocellulosic biomass and/or to dissolve lignin are provided.

One embodiment of a method for treating lignocellulosic biomass includesdispersing a lignocellulosic biomass in an aqueous solution comprising asulfonic acid, such as p-toluenesulfonic acid. The concentration of thesulfonic acid in the solution is higher than its minimal hydrotropeconcentration so that lignin in the lignocellulosic biomass isdissolved. The solution is maintained at a temperature and for a timesufficient to dissolve at least 10 wt. % of the lignin in thelignocellulosic biomass. The solution and the dispersed lignocellulosicbiomass can then be separated into a spent acid solution comprisingdissolved lignin and a water-insoluble cellulose-rich solids fractionreferred to as water-insoluble lignocellulosic solid residues (LCSR).

Optionally, the spent acid solution and/or the water-insolublelignocellulosic solid residues can then the further processed. Forexample, the spent acid solution can be further processed byprecipitating out lignin nanoparticles and/or by converting dissolvedsugars into furans, which can be separated from the spent acid solution.The lignocellulosic solid residues can be further processed intolignocellulosic microfibrils, lignocellulosic nanofibrils, or acombination thereof via mechanical fibrillation and/or by convertingthem into sugars via hydrolysis.

Other principal features and advantages of the invention will becomeapparent to those skilled in the art upon review of the followingdrawings, the detailed description, and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Illustrative embodiments of the invention will hereafter be describedwith reference to the accompanying drawings, wherein like numeralsdenote like elements.

FIG. 1 is a flow chart showing one embodiment of a wood processingmethod that includes a lignocellulosic biomass fractionation usingsulfonic acid hydrotropes.

FIG. 2A is a graph of L_(R), the fractions of lignin retained on thewater insoluble solids of Example 2. FIG. 2B is a graph of X_(R), thefractions of xylan retained on the water insoluble solids of Example 2.

FIG. 3A is a graph of the cellulose enzyme digestibility for NE222fractionated solids that were fractionated using a p-TsOH concentrationof 75 wt % at 65° C. for different times. FIG. 3B is a graph of thecellulose enzyme digestibility for NE222 fractionated solids that werefractionated using a p-TsOH concentration of 70 wt % for 35 min atdifferent temperatures.

FIG. 4A is an atomic force microscope (AFM) image of separated LCNCparticles for sample P85T80t20 from Example 7. FIG. 4B is an AFM imageof separated LCNC particles for sample P80T80t20 from Example 7. FIG. 4Cis an AFM image of separated LCNC particles for sample P65T80t20 fromExample 7.

FIG. 5 shows the AFM height measured distributions for samplesP85T80t20, P80T80t20, and P65T80t20 from Example 7.

FIG. 6A is an AFM image of separated LCNF particles for sample P50T80t20from Example 8. FIG. 6B is an AFM image of separated LCNF particles forsample P65T80t20 from Example 8. FIG. 6C is an AFM image of separatedLCNF particles for sample P80T80t20 from Example 8.

FIG. 7 is a graph showing AFM height measured distributions for LCNFsamples P80T80t20, P65T80t20, and P50T80t20 from Example 8.

FIG. 8A is an AFM image of the LCNFs from P50T80t20 of Example 8 afterone pass through the chamber of a microfluidizer. FIG. 8B is an AFMimage of the LCNFs of Example 8 after three passes through the chamberof a microfluidizer. FIG. 8C is an AFM image of the LCNFs of Example 8after five passes through the chamber of a microfluidizer. FIG. 8D is anAFM image of the LCNFs of Example 8 after seven passes through thechamber of a microfluidizer. FIG. 8E is an AFM image of the LCNFs ofExample 8 after nine passes through the chamber of a microfluidizer.

FIG. 9 shows the AFM height measured distributions for the LCNFs ofFIGS. 8A-8E.

FIG. 10A is an image of the whisker-like cellulose nanofibrils ofExample 9.

FIG. 10B is an enlarged image of the whisker-like cellulose nanofibrilsof Example 9.

FIG. 11 is another image of the whisker-like cellulose nanofibrils ofExample 9.

FIG. 12 is a graph showing lignin particle sizes measured by dynamiclight scattering in a spent liquor at different acid dilution ratios, asdescribed in Example 10.

FIG. 13 is a graph of conductivity measurements versus concentration foraqueous p-TsOH solutions, as described in Example 10.

FIG. 14 is an AFM topographic image of the lignin particles of Example11 deposited on a fresh mica sheet.

FIG. 15 is a graph showing the height profile of the lignin particles ofFIG. 14.

FIG. 16A is an AFM image of lignin particle aggregates in a supernatantcentrifuged at a centrifuge speed of 3000 g with a lateral size ofapproximately 600 nm, as described in Example 11. FIG. 16B is an AFMimage of small lignin particle aggregates in a supernatant centrifugedat a centrifuge speed of 10000 g. FIG. 16C is an AFM image of ligninparticle aggregates in a supernatant centrifuged at a centrifuge speedof 15000 g

FIG. 17 is a graph of AFM height measurements of the LCNF samples ofFIGS. 16A-16C.

FIG. 18 is a graph of LNP particle size measured by dynamic lightscattering as a function of centrifugation speed.

FIG. 19A is a graph of LNP particle size measured by dynamic lightscattering as a function of dilution speed for the LNPs of Example 12.FIG. 19B is an AFM height measurement of the LNPs of FIG. 19A atdifferent dilution rates.

FIG. 20A is an AFM image of lignin aggregates formed using a dilutiontime/min of 0.05, as described in Example 12. FIG. 20B is an AFM imageof lignin aggregates formed using a dilution time/min of 1.5. FIG. 20Cis an AFM image of lignin aggregates formed using a dilution time/min of240.

FIG. 21A is a graph of LNP particle size and zeta potential for the LNPsof Example 12 as a function of solution pH. FIG. 21B is a graph of AFMheight measurements for the LNPs of FIG. 21A at different pH values.

FIG. 22A is an AFM image of the LNCs of Example 12 at a solution pH of11.5. FIG. 22B is an AFM image of the LNCs of Example 12 at a solutionpH of 7.5. FIG. 22C is an AFM image of the LNCs of Example 12 at asolution pH of 5.4.

FIG. 23A is a graph of LNP particle size and zeta potential for the LNPsof Example 12 as a function of NaCl concentration. FIG. 23B is a graphof AFM height measurements for the LNPs of FIG. 23A at different NaClconcentrations.

FIG. 24A is an AFM image of the LNPs of Example 12 for an NaClconcentration of 10 mM. FIG. 24B is an AFM image of the LNPs of Example12 for an NaCl concentration of 33 mM. FIG. 24C is an AFM image of theLNPs of Example 12 for an NaCl concentration of 5 mM.

FIG. 25 is a graph of LNP particle size and zeta potential for the LNPsof Example 12 as a function of dissolved lignin content.

FIG. 26 is a graph of the colloidal stabilities of LNPs in a supernatantfrom a centrifuge and in a suspension of re-suspended precipitates overa period of two weeks.

FIG. 27 is a graph of the zeta potential of LNPs in a supernatant from acentrifuge and in a suspension of re-suspended precipitates over aperiod of two weeks.

FIG. 28A is an AFM image of the LNPs in a supernatant at t=0 hours. FIG.28B is an AFM image of the LNPs in a supernatant at t=336 hours, asdescribed in Example 14.

FIG. 29 is a graph of AFM height measurements of the samples of FIGS.28A and 28B.

FIG. 30A is an AFM image of LNPs from a suspension of re-suspendedprecipitates. FIG. 30B is an AFM image of LNPs from a suspension ofre-suspended precipitates from a centrifuge at t=0.

FIG. 31 is a graph of AFM height measurements of the LNPs in FIG. 30A att=0 and in FIG. 30B at t=336 hours.

FIG. 32A shows an optical micrograph image (left panel) and a scanningelectron microscope (SEM) image (right panel) of MDF fibers beforedelignification. FIG. 32B shows an optical micrograph (left panel) andan SEM image (right panel) of MDF fibers after delignification.

FIG. 33A shows and optical micrograph (left panel) and an SEM image(right panel) of delignified and refined MDF fibers at a CanadianStandard Freeness (CSF) of 650 mL. FIG. 33B shows an optical micrograph(left panel) and an SEM image (right panel) of delignified and refinedMDF fibers at a Canadian Standard Freeness (CSF) of 450 mL.

FIG. 34A is a graph of the tensile index as a function of CSF for abirch MDF sheet. FIG. 34B is a graph of the failure strain as a functionof CSF for a birch MDF sheet.

FIG. 35A is a graph of the solubility of alkali technical lignin as afunction of p-TsOH concentration. FIG. 35B is a graph of the solubilityof alkali technical lignin as a function of solution temperature.

FIG. 36A is an AFM image of precipitated LNPs from sample P40T35. FIG.36B is an AFM image of precipitated LNPs from sample P50T65. FIG. 36C isan AFM image of precipitated LNPs from sample P55T80.

FIG. 37 is a graph of AFM height measurements of the samples of FIGS.36A-36C.

FIG. 38A is the first part of Table 1 from Example 2. FIG. 38B is thesecond part of Table 1 from Example 2. Table 1. Shows the chemicalcompositions of p-TsOH fractionated poplar NE222 samples under differenttreatment conditions. The numbers in the parentheses are componentyields based on component in the untreated NE222. ¹ (Pxx, Txx, txx)stands for p-TsOH concentration in wt %, reaction temperature in ° C.and reaction duration in min. ²Yields are based on xylan content inNE222. HMF in spent liquors were not detectable.

DETAILED DESCRIPTION

Various embodiments of the inventions described herein are based, atleast in part, on the discovery that certain organic solid acids havehydrotropic properties, and are capable of efficiently solubilizinghydrophobic lignin at low temperatures (below the boiling point ofwater) in a short period of time. As such, a low-energy, low-cost andefficient lignocellulosic biomass fractionation process can be carriedout using these easily recyclable organic solid acids, which includep-toluenesulfonic acid (p-TsOH), in aqueous solution, at lowtemperatures and atmospheric pressures. The fractionation produces asolid fraction that contains mainly cellulose and some hemicellulosesand a liquid fraction that contains dissolved lignin and somehemicellulosic sugars. The solid fraction can be used with or withoutbleaching to produce wood fibers, and/or cellulose micro- ornanomaterials, and/or sugars (through hydrolysis), and/or valuablechemicals, such as furfural. The cellulose micromaterials andnanomaterials include lignocellulosic micro-fibrils (LCMFs) orlignocellulosic nano-fibrils (LCNFs) with controllable lignin contentson their surfaces (e.g., coated via precipitation) or in theircellulosic matrices (containing native lignin) from the fractionatedsolids. The solubilized lignin in the liquid fraction can be separatedas lignin nanoparticles through the precipitation of solubilized ligninby diluting the spent acid solution with water to a concentration belowthe minimal hydrotrope concentrations (MHC). The obtained ligninnanoparticles (LNPs) comprise oblate spheroids with tunable morphologyand surface properties. Some embodiments of the LNPs have diametersranging from, for example, 150˜3000 nm and thicknesses ranging from, forexample, 3˜50 nm. The properties of the lignin LNPs can be tailored bycontrolling the pretreatment conditions of the biomass and the dilutingfactors of the spent acid solutions, as illustrated in the Examples.

Lignocellulosic Biomass:

As used herein, the term lignocellulosic biomass refers to materialsfrom plant cell wall that primarily includes lignin and hemicelluloses,as well as cellulose. Lignocellulosic biomass may be, for example, wood,grasses, and agriculture crop stems or stalks. Wood biomass can be ahardwood or a softwood or a mixture thereof. The wood may be provided inmilled or chip form. However, for the production of wood fibers, woodchips may be more suitable.

Lignocellulose Nanocrystals (LCNCs):

As used herein, the term LCNC refers to elongated rod-like crystallinelignin-containing cellulose nanoparticles. LCNCs comprise cellulosechains produced from lignocellulosic biomass via fractionation. LCNCscan be in the form of a single cellulose crystallite or a bundle ofcellulose crystallites, and may or may not contain hemicelluloses. LCNCsare generally characterized by lengths in the range from about 60 toabout 1000 nm; widths in the range from about 5 to about 50 nm; andcorresponding aspect ratios in the range from about 1 to about 200.

Lignocellulose Nanofibrils (LCNFs):

As used herein, the term LCNF refers to long flexible fiber-likelignin-containing cellulose nanoparticles. LCNFs can be branched orunbranched and can take the form of a network of flexible fiber-likenanoparticles. LCNFs comprise cellulose, hemicellulose, and lignin. Thefiber-like lignocellulose particles are generally characterized bylengths in the range from about 100 to about 5,000 nm; widths in therange from about 5 to about 200 nm; and corresponding aspect ratios inthe range from about 2 to about 1,000.

Lignocellulose Fibers (LCFs):

As used herein, the term LCF refers to lignin-containing celluloseparticles. LCFs comprise cellulose, hemicellulose, and lignin. LCFs aregenerally characterized by lengths in the range from about 0.05 to about3 mm; widths in the range from about 5 to about 50 μm; and correspondingaspect ratios in the range from about 2 to about 500.

Lignocellulose Microfibers (LCMFs):

As used herein, the term LCMF refers to lignin-containing cellulosemicroparticles. LCMFs comprise cellulose, hemicelluloses, and lignin.LCMFs are characterized by lengths in the range from about 5 to about100 μm; widths in the range from about 0.1 to about 10 μm; andcorresponding aspect ratios in the range from about 2 to about 500.

Lignocellulosic Solid Residues (LCSR):

As used herein, the term LCSR refers to a solid material composed ofLCFs, LCMFs, or a combination thereof. In the present methods, LCSRs arepart of the solid material remaining after the biomass fractionation.

Lignin Nanoparticles (LNPs):

As used herein, the term LNP refers to lignin nanoparticles. LNPs can bein the form of single lignin macro molecule or aggregates of ligninmacro molecules. LNPs are generally characterized by dimensions in therange from 1 nm to 10 μm (e.g., from 10 nm to 500 nm) and may have anoblate spheroid shape.

The lignocellulosic biomass fractionation methods utilize sulfonicacids, such as methenesulfonic acid, and, in some embodiments, aromaticsulfonic acids, such as p-toluenesulfonic acid, benzenesulfonic acid,xylenesulfonic acid, and mixtures of two or more thereof, or mixtures ofone or more thereof with their salts.

One aspect of the present invention uses a concentrated organic sulfonicacid, rather than, or in addition to, sulfonic (aromatic) salts, tosolubilize lignin for wood fractionation. With sulfonic aromatic acids,the process can be conducted at low temperatures using a very shortreaction time. By way of illustration, various embodiments of thelignocellulosic biomass fractionation are carried out at temperatures ofno greater than 100° C. This includes embodiments of the lignocellulosicbiomass fractionation that are carried out at temperatures of no greaterthan 90° C. and further includes embodiments of the lignocellulosicbiomass fractionation that are carried out at temperatures of no greaterthan 80° C. For example, the lignocellulosic biomass fractionation canbe carried out at temperatures in the range from 30° C. to 85° C.,including temperatures in the range from 50° C. to 85° C., and furtherincluding temperatures in the range from 60° C. to 80° C. However,temperatures outside of these ranges can be used, depending on thedesired degree of lignin dissolution. By way of further illustration,various embodiments of the lignocellulosic biomass fractionation can becompleted in a reaction time of 5 hours or less. This includesembodiments of the lignocellulosic biomass fractionation that arecompleted in a reaction time of 4 hours or less, 3 hours or less, 2hours or less, and 1 hour or less. For example, the lignocellulosicbiomass fractionation can be carried out for a reaction time in therange from 15 minutes to 90 minutes, including reaction times in therange from 20 minutes to 60 minutes. However, reaction times outside ofthese ranges can be used, depending on the desired degree of lignindissolution. As used herein, the reaction time refers to the timebetween the onset of the solubilization of the lignin in the biomass bythe sulfonic acid and the cessation of the lignin solubilization whenthe sulfonic acid concentration in the fractionation solution is broughtbelow its minimal hydrotrope concentration. By way of illustration, thesolubilization of lignin using p-TsOH can be terminated by decreasingthe acid concentration to below about 11.5 wt. %.

In the lignocellulosic biomass fractionation solution, the sulfonic acidhas a concentration above its minimum hydrotrope concentration, so thatit solubilizes lignin, which is hydrophobic, in the fractionationsolution. Generally, the sulfonic acid has a concentration that issignificantly greater than the minimum hydrotrope concentration in orderto enhance lignin solubilization. By way of illustration, in variousembodiments of the lignocellulosic biomass fractionation method, thefractionation solution has a sulfonic acid (for example p-TsOH)concentration of at least 15% (or above MHC). This includes embodimentsof the methods in which the fractionation solution has a sulfonic acidconcentration of at least 50%, at least 60%, at least 65%, at least 70%,at least 75%, and at least 80%. For example, sulfonic acidconcentrations in the range from about 50% to about 85%, including inthe range from about 65% to about 80%, can be used. However,concentrations outside of these ranges can be used, depending upon thedesired degree of lignin dissolution.

The lignocellulosic biomass fractionation process can solubilize themajority of the lignin in a lignocellulosic biomass sample without theneed for an initial pulping to reduce the lignin content prior to thesulfonic acid treatment. In various embodiments of the lignocellulosicbiomass fractionations, at least 10% of the lignin in the biomass issolubilized during the fractionation. This includes embodiments of thefractionations that solubilize at least 45%, at least 50%, at least 55%,at least 60%, at least 65%, at least 70%, at least 75%, at least 80%,and at least 90% of the lignin in the biomass. However, percentages oflignin solubilization outside of these ranges can also be achieved. Thesolubilization of the lignin can also be quantified in terms of grams oflignin dissolved per 100 g of solution. In some embodiments of thelignocellulosic biomass fractionation, at least 2 g lignin/100 g ofsolution is dissolved.

One aspect of the invention provides a low temperature and ambientpressure wood processing method that includes lignocellulosic biomasspre-treatment, followed by the lignocellulosic biomass fractionationand, optionally, post-fractionation processing that can be carried outfor producing fibers, and/or LCNF or LCMF, and/or sugars, and/or LNPwith recovery of acid, as schematically shown in FIG. 1. In alignocellulosic biomass pre-treatment step, lignocellulosic biomass 102,such as wood, is size-reduced 104 using, for example, low mechanicalenergy input disk milling conducted at temperatures above lignin glasstransition temperature. Additionally, lignocellulosic biomass, such aswood chips, can be fibrillated using, for example, mechanicalfibrillation, in order to increase exposed lignin at the fiber surfacesprior to lignocellulosic biomass fractionation. Another pre-treatmentstep that can be included in the process is prehydrolysis using hotwater to improve hemicellulose removal and delignification. Thesize-reduced, fibrillated, and/or prehydrolyzed lignocellulosic biomassis then fractionated 106 using a sulfonic aromatic acid, such asp-TsOH,as a hydrotrope 108 for the lignin in the biomass at a low temperature(for example, approximately 80° C. or lower) for a short time (e.g., 20minutes to one hour). After subsequent filtration and, optionally,washing 110, the spent acid solution from the lignocellulosic biomassfractionation 106 can be cycled back to the fractionation and directlyreused 112. After several runs, dissolved solids, such as lignin andsugars, accumulate in the spent acid solution. These may be removed tofurther reuse the acid. Dissolved lignin in the filtrate can be easilyremoved by precipitation initiated through dilution with water 114. Thediluted spent liquor can then be reconcentrated to convert dissolvedsugars, such as xylose, into furans, such as furfural, throughdehydration (e.g., evaporation) 116 using the sulfonic aromatic acid inthe liquor as a catalyst. Reconcentration can also facilitate theremoval of excess sulfonic aromatic acid 118 from the system throughcrystallization 116 when desirable. The furans 122 can be separatedthrough distillation and dehydration 120. The remaining acid solutioncan then be cycled back to reused in the lignocellulosic biomassfractionation 106. The separated and subsequently washed water-insolublesolids contain lignocellulosic solid residues (LCSRs), andlignocellulosic nanocrystals (LCNC). Optionally, the LCNCs can beseparated from the LCSRs by dialysis. The LCSR, with or withoutseparating LCNC, can be used for producing chemical pulp fibers such asdissolving pulps 124 after bleaching 126, lignocellulose micro and/ornanofibrils (LCMF and/or LCNF) 128 with mechanical fibrillation 130, orsugars 132 through (enzymatic) hydrolysis 134.

Another aspect of the inventions provides methods for the production ofLCNCs, LCNFs, LCMFs, and/or wood fibers from fractionated waterinsoluble solids, as described above and illustrated in FIG. 1. Asillustrated in Example 7, the relative amount of LCNFs or LCMFs producedcan be controlled by the severity of biomass fractionation. Asillustrated in Example 8, low severity fractionation conditions tend tofavor the production of long LCNFs.

Another aspect of the inventions provides methods for the production ofLNPs with controllable sizes and shapes directly from the spent liquorfrom the biomass fractionation simply by precipitation after waterdilution, as illustrated in FIG. 1. Processing conditions that can beused to control the size and morphology of the LNPs include the rate atwhich the spent fractionation solution is diluted and the severity ofthe biomass fractionation reaction conditions. The pH of the solutioncan also be used to tailor LNP size, whereby changing the pH of thespent liquor from the biomass fractionation to a low value (e.g., ≤3) ora high value (e.g., ≥10) results in a larger LNP size.

Another aspect of the inventions provides methods for the production ofvaluable chemicals, such as furans (e.g., furfurals), from the dissolvedsugars, as illustrated in FIG. 1.

As used in this disclosure, any concentrations that are provided as apercentage (%) refer to a weight percentage (wt %), unless otherwiseindicated.

EXAMPLES

Materials Used

p-TsOH was purchased from Sigma-Aldrich (St. Louis, Mo.). Poplar NE-222(Populus deltoides Bartr. ex Marsh×P. nigra L.) were harvested from HugoSauer Nursery in Rhinelander, Wis., USA, and provided by the US ForestService, Northern Research Station. The NE222 logs were debarked andchipped at the US Forest Service, Forest Products Laboratory.Douglas-fir (Pseudotsuga menziesii) wood chips were collected byWeyerhaeuser Company from a pulp mill in Washington State. The NE222 andDouglas-fir wood chips were ground to a 20-mesh size using a Wiley mill.

White birch logs were obtained from the US Forest Service, RhinelanderExperimental Forest, Northern Research Station. The logs were harvestedin February 2016 and had breast height diameter of 6-8 inches. The logswere peeled in March 2016 and immediately chipped at the US ForestService, Forest Products Laboratory. The chips were screened using 1¼″square holes. Oversized chips were re-chipped to increase recovery.

Another softwood feedstock originated from Timber Products in Yreka,Calif. The feedstock are residuals from a veneer operation and comprisepredominantly ponderosa pine with a small percentage of sugar pine.During veneer processing, all logs were debarked. On-spec logs werepeeled for veneer, while defective logs were sent to the byproductchipper. After veneer peeling, the residual bolts were chipped in awhole log chipper. The outputs of the two chipper lines were then mixedand screened. The undersized particles were sent to particle boardproduction, while the oversized particles were re-chipped. The TimberProducts specification for the resulting residual chips is less than 1%bark.

Example 1: Wood Fractionation Using a Concentrated p-TsOH Solution

Concentrated p-TsOH aqueous solutions at desired mass concentrationswere prepared using de-ionized (DI) water. For studies using Wileymilled poplar and Douglas-fir wood particles, 50 mL of a prepared acidsolution was added into a 150 mL flask and heated to the preset reactiontemperature on a heating plate. A 5 g oven dry (OD) quantity of woodparticles was transferred into the flask. The flask was then placed on ashaker at 200 rpm. At the end of the preset reaction time (between 5-60min), the reaction was terminated by adding an appropriate amount of DIwater to dilute the concentration down to 40 wt %. The solids wereseparated from the liquor using vacuum filtration. The filtrate wascollected to produce LNP through dilution. The solids were thoroughlyrinsed using DI water until the pH of the rinse filtrate did not change.The final rinsed solids were collected for compositional analyses.

Example 2: Fractionated Solids of NE222

The chemical compositions of the original, as well as the chemicallyfractionated solids of NE222, were analyzed by the Analytical Chemistryand Microscopy Lab (ACML) at the US Forest Service, Forest Products Lab,as described previously (Davis 1998; Luo et al. 2010). As listed inTable 1, FIGS. 38A and 38B, concentrated p-TsOH solution was able tosolubilize a substantial (up to 90.7%) amount of poplar NE222 (hardwood) lignin using a very short reaction time of approximately 30 min ata temperature 80° C. or lower. This amount of lignin removal isequivalent to chemical pulping that is often conducted at temperaturesof 170° C. for 2 hours with fairly high alkali loadings of approximately25% on wood. Dissolution of xylan was also substantial. Glucan loss,however, was minimal, especially at a temperature of 65° C. or lower.Using an extended reaction time of 60 min or longer can compensate forreduced reaction severity at low temperatures, e.g., 65° C., to achieveimproved lignin and hemicellulose dissolution while maintaining a highglucan yield. Lignin condensation occurred at 80° C. with reaction timesof 35 min or longer. To achieve desired fractionation, the reactionseverity can be adjusted. This is demonstrated in Eqs. (1a, b) and (2a,b). This is important to the production of pulp fibers, and especiallyfor dissolving pulp fibers which require high cellulose yield, goodstrength, and minimal lignin and hemicellulose content.

$\begin{matrix}{{L_{R} = {{\left( {1 - \theta^{\prime} - \theta_{R}^{\prime}} \right)e^{- {CDF}}} + {\theta^{\prime} \cdot e^{{- f} \cdot {CDF}}} + \theta_{R}^{\prime}}}{with}} & \left( {1a} \right) \\{{CDF} = {{\exp\left( {\alpha^{\prime} - \frac{E^{\prime}}{RT} + {\beta^{\prime}C}} \right)}{C \cdot t}}} & \left( {1b} \right) \\{{X_{R} = {{\left( {1 - \theta - \theta_{R}} \right)e^{- {CHF}}} + {\theta \cdot e^{{- f} \cdot {CHF}}} + \theta_{R}}}{with}} & \left( {2a} \right) \\{{CHF} = {{\exp\left( {\alpha - \frac{E}{RT} + {\beta\; C}} \right)}{C \cdot t}}} & \left( {2b} \right)\end{matrix}$where L_(R) and X_(R) are fractions of lignin and xylan retained on thewater insoluble solids (WIS), respectively. θ′ and θ are the fractionsof bulk fast solubilization lignin and xylan, respectively, θ′_(R) orθ_(R) are the fractions of unsolubilized residue lignin and xylan, f′ orf are the ratio of lignin or xylan solubilization between the slow andbulk fast lignin or xylan, α′, α and β′, β are adjustable parameters, E′and E are activation energy, R is the universal gas constant (8.314 Jmol⁻¹ K⁻¹), T is temperature in kelvins, C is initial p-TsOHconcentration in mol⁻¹, and t is dissolution time in min.

Eqs. (1) and (2) fit to the experimental data very well, as shown inFIGS. 2A and 2B. Furthermore, the dissolved carbohydrates in the spentliquor were mainly in the form of monomeric sugars. Degradation ofxylose to furfural was minimal, less than 2% for most runs due to therapid and low-temperature p-TsOH fractionation (Table 1 in FIG. 38A andFIG. 38B). Total xylan recovery from both the retained xylan and thedissolved xylose (not including oligomeric xylose in the spent liquor)were near 90% based on xylan content in untreated poplar NE222. Aceticacid concentration in the spent liquor was very low, at less than 1.5g/L. These data demonstrate that p-TsOH fractionation can alsoefficiently recover hemicellulosic sugars.

Example 3: Fractionated Solids of Douglas-Fir

Fractionations were also carried out for Douglas-fir (softwood) aslisted in Table 2. p-TsOH was less effective in solubilizing softwoodlignin. A maximum of approximately 60% of Douglas-fir lignin wassolubilized using a p-TsOH concentration of 80 wt % for 20 min at 80° C.An extended reaction time of 60 min caused lignin condensation, andslightly increased the residual lignin in the solids.

TABLE 2 Chemical compositions of p-TsOH fractionated Douglas-fir solidsunder different treatment conditions. The numbers in the parentheses arecomponent yields. Solids Douglas- yield Glucan Xylan Mannan Lignin fir¹(%) (%) (%) (%) (%) untreated 100 34.3 7.2 7.7 31.0 P70T80t20 70.1  52.0(106.4) 3.8 (37.3) 6.2 (56.0) 32.6 (73.5) P75T65t60 65.1  58.9 (111.9)3.9 (35.1) 7.0 (58.7) 31.6 (66.2) P75T80t20 64.4 48.3 (90.7) 3.3 (29.6)6.0 (49.6) 30.7 (63.7) P80T80t20 56.8 54.4 (90.1) 3.3 (26.3) 5.5 (40.7)25.2 (46.1) P80T80t35 53.4 55.4 (86.4) 2.5 (18.9) 5.0 (35.1) 24.9 (42.8)P80T80t60 53.5 62.2 (97.1) 2.7 (19.8) 5.0 (34.4) 26.3 (45.3) ¹(Pxx, Txx,txx) stands for p-TsOH concentration in wt %, reaction temperature in °C. and reaction duration in min.

Example 4: Sugar Production from Fractionated Solids

The fractionated solids of NE222 were found to be enzymaticallydigestible. Therefore, the present methods using aromatic acids can beapplied for sugar/biofuel production from lignocellulosic biomass usingvery low temperatures and at atmospheric pressure with short reactiontimes. When enzymatic hydrolysis was conducted using a commercialcellulase (CTec3) loading of 20 FPU/g glucan in acetate buffer of pH5.5, cellulose enzymatic digestibility of over 90% was achieved, asshown in FIGS. 3A and 3B, for substrates produced at the more severeconditions, such as P75T65t35, P75T65t60, and P70T80t20. ((Pxx, Txx,txx) stands for p-TsOH concentration in wt %, reaction temperature in °C. and reaction duration in min.)

Sugar production from fractionated Douglas-fir softwood was also carriedout, but with slightly poorer performance compared with that from NE222.

Solubilized sugars in the spent acid solution, mainly hemicellulosicsugars, can be converted into furan, as discussed in Example 2 (Table 1in FIGS. 38A and 38B).

Example 5: Dissolving Pulp Fiber Production from Poplar Wood

The fractionated solids have the potential for wood fiber production,especially dissolving grade pulp fibers, due to the substantial removalof hemicelluloses by the acid. One of the key measures of dissolvingpulp is the pulp viscosity or DP. A separate set of fractionationexperiments were conducted. Pre-hydrolysis using hot-water (HW) at 170°C. for 50 min (corresponding to a P-factor of 500) was applied to poplarwood chips to improve hemicellulose removal and delignification. Woodchips were used in these experiments, since Wiley milling shortens woodtracheid and therefore is not suitable for fiber production. The HWprehydrolyzed wood chips were then fractionated using a p-TsOH solutionat 80 wt % concentration at 80° C. for 20 min based on the results shownin Table 1, FIGS. 38A and 38B. It was found that HW treatment did notimprove lignin solubilization (Table 3). An 8-inch hand-driven disk mill(Andritz Sprout-Bauer Refiner, Springfield, Ohio) was also used tofiberize the wood chips to improve delignification in the subsequenttreatment, with and without HW treatment, as shown in Table 3.

HW prehydrolysis, when applied alone, was relatively effective insolubilizing hemicelluloses (Table 3). When milling was applied, boththe HW and non-HW samples behaved similarly; both allowed significantdelignification and both types had similar hemicellulose contents(comparing Mill+P80T80t20 with HW+Mill+P80T80t20 in Table 3). Thisindicates that HW prehydrolysis is not necessary for the presentmethods. However, size reduction processes, such as milling, may bedesirable for achieving a high degree of delignification.

TABLE 3 Chemical compositions of p-TsOH fractionated (at P80T80t20)NE222 wood chips with and without hot-water prehydrolysis and/or millingfor dissolving pulp production. The numbers in the parentheses arecomponent yields. Solids yield Glucan Xylan Mannan Lignin NE222 ¹ (%)(%) (%) (%) (%) Untreated 100.0 46.5 15.4 4.5 23.7 HW 93.2 49.4 (98.9)7.1 (43.2) 1.6 (33.6)  25.6 (100.0) P80T80t20 75.6 60.4 (98.2) 7.3(35.7) 2.8 (48.0) 18.6 (59.1) HW + P80T80t20 75.3 60.5 (97.9) 6.1 (29.8)2.3 (38.5) 20.0 (63.5) Mill + P80T80t20 56.9 71.9 (87.9) 4.4 (16.4) 3.1(39.5) 10.8 (14.2) HW + Mill + P80T80t20 54.2 73.4 (85.6) 4.2 (14.7) 3.0(36.8)  5.3 (12.0) HW + P80T80t20 + Bleach 51.0 84.5 (92.7) 4.5 (14.9)2.3 (26.0) 1.0 (2.0) Mill + P80T80t20 + Bleach 43.1 90.0 (83.4) 4.2(11.8) 2.4 (22.7) 0.2 (0.3) HW + Mill + P80T80t20 + Bleach 41.4 92.9(82.6) 3.6 (9.6)  2.2 (20.5) 0.2 (0.3) ¹ HW stands for hot-water at 170°C. for 50 min. (Pxx, Txx, txx) stands for p-TsOH concentration in wt %,reaction temperature in ° C. and reaction duration in min.

Chlorite bleaching was applied to three p-TsOH (P80T80t20) fractionatedsolid samples: with HW only, with milling only, and with both HW andmilling as listed in Tables 4 and 5. Bleaching entailed mixing 2 g driedsolid sample, 65 mL of 75° C. DI-water, 0.5 mL of glacial acetic acidand 0.6 g of sodium chlorite in a beaker for 4 hours. Additionalreagents, consisting of 0.5 ml of glacial acetic acid and 0.6 g ofsodium chlorite, were added at 1, 2 and 3 hours. The resulting bleachedpulp was washed by vacuum filtration with DI-water until the pH of thefiltrate was close to neutral, and then dried at 105° C. The samplewithout milling (HW+P80T80t20+Bleach) contained a substantial amount oflignin, so the bleaching was repeated on a new sample using doublequantities of sodium chlorite, which resulted in a relatively low ligninlevel. The two samples with milling had relatively low xylan contents ofapproximately 4% or less, and lignin contents of 0.2% after bleaching.The pulp viscosities of these three samples were between 360 and 430(mL/g), as listed in Table 4, and are slightly lower than the range of450-500 (mL/g) for typical dissolving pulp fibers. Careful examinationof the data in Table 1 of FIGS. 38A and 38B, shows that a low reactiontemperature can result in low glucan degradation, or lessdeploymerization of cellulose, which can be used to improve theviscosity of the resultant pulp. The reduced delignification, due to alower temperature or low p-TsOH concentration, can be compensated for byusing a longer reaction time such as 60 min (comparing P75T80t20 withP75T65t60).

TABLE 4 Bleached pulp viscosity and DP. Intrinsic NE222 viscosity (mL/g)DP HW + P80T80t20 + Bleach 427.5 ± 0.7 587.6 ± 1.1 Mill + P80T80t20 +Bleach 377.7 ± 0.5 512.4 ± 0.9 HW + Mill + P80T80t20 + Bleach 357.5 ±0.7 482.1 ± 0.4

Another set of experiments was carried out to evaluate the feasibilityof reducing acid concentration for dissolving pulp production using thesame refined poplar fibers described above without HW pretreatment. Ascan be clearly seen from Table 5, a low p-TsOH concentration can becompensated for with a longer reaction. Both the pulp viscosity andxylan content after chlorite bleaching are suitable for dissolving pulp.

TABLE 5 Chemical composition and pulp viscosity of bleached poplar NE222pulp delignified by p-TsOH. Solids Sample yield Viscosity Glucan XylanMannan Lignin Label¹ (%) (mL/g) (%) (%) (%) (%) Poplar 45.7 14.9 4.623.4 NE222 P85T80t20 64.7 70.3 5.7 3.2 8.8 (post- 45.2 442 75.7 5.8 3.30.8 bleaching) P65T80t180 60.7 71.4 4.3 3.0 12.4 (post- 43.7 522 74.84.7 3.6 0.7 bleaching) ¹(Pxx, Txx, txx) stands for p-TsOH concentrationin wt %, reaction temperature in ° C. and reaction duration in min.

Example 6: Production of Dissolving Pulp from Birch Wood

To further evaluate p-TsOH fractionation for dissolving pulp production,birch wood chips were used that are used widely for pulp production andcontained a minimal level of mannan. Medium density fiberboard (MDF)type fibers were produced from the birch wood chips in a 12″ pressurizeddisk refiner (Sprout-Bauer, model 1210P, Muncy, Pa., USA) bypre-steaming the wood chips at 165° C. or steam pressure 0.62 MPa (105Psia). The disk plate pattern was D2B505 with a gap of 7/1000 inches.The wood chip feeding rate was approximately 1 kg/min. The MDF processhas three distinct features uniquely suited for this study: (1) lowenergy cost in fiberization by pre-steaming above the lignin glasstransition temperature to initiate fiber separation in the middlelamella; (2) as a result, a major portion of the lignin is exposed onthe resulting fiber surface, which should facilitate solubilization oflignin by p-TsOH; (3) minimal fiber cutting that can avoid unnecessaryreduction of DP or pulp viscosity.

TABLE 6 Chemical compositions of p-TsOH fractionated birch MDF fordissolving pulp and LCNF production. The numbers in the parentheses arecomponent yields (g/100 g wood). Solids yield Glucan Xylan Mannan LigninBirch MDF ¹ (%) (%) (%) (%) (%) Untreated 100.0 38.7 ± 0.88 21.5 ± 0.021.9 ± 0.03 20.2 ± 0.67  P50T80t20 56.66 59.2 ± 0.96 15.0 ± 0.28 2.4 ±0.02 16.0 ± 0.47  (33.6) (8.5) (1.3) (9.0) P65T80t20 54.15 62.0 ± 0.7414.0 ± 0.12 2.6 ± 0.01 11.6 ± 0.32  (33.6) (7.6) (1.4) (6.3) P75T80t2053.76 65.3 ± 1.59 12.6 ± 0.21 2.3 ± 0.11 9.5 ± 0.23 (35.1) (6.7) (1.2)(5.1) P80T80t20 51.31 67.7 ± 0.20 12.2 ± 0.08 2.50 ± 0.07  7.2 ± 0.18(34.7) (6.2) (1.3) (3.7) P85T80t20 52.39 67.6 ± 2.69 11.2 ± 0.43 2.2 ±0.10 8.0 ± 0.12 (35.4) (5.8) (1.2) (4.2) P80T65t60 53.12 65.9 ± 0.0113.3 ± 0.02 2.9 ± 0.01 9.1 ± 0.03 (35.0) (7.1) (1.5) (4.8) P80T65t60-46.63 77.9 ± 2.07 13.6 ± 0.38 2.7 ± 0.26 1.1 ± 0.06 bleached

The washed fractionated solids of P80T65t60 were used for dissolvingpulp production. It appeared that the hydrolysis time of 60 min was tooshort when the temperature was reduced to 65° C. resulting in ahydrolyzed sample with very high xylan and lignin content of over 13 and9%, respectively. After bleaching, the sample still had an undesirablyhigh xylan content, while lignin was reduced to approximately 1%. Theviscosity of the bleached pulp was 392 mL/g with DP of 533. The xylan inthe sample contributed to the low DP. A long reaction time would addressthe problem associated with high lignin and xylan contents as shown inTable 5.

Example 7: Production of Lignocellulosic Nanocrystals from Birch Wood

The MDF fibers described in example 6 were used for the integratedproduction of LCNCs with LCNFs or LCMFs (depending on the extent ofmechanical fibrillation and the severity of p-TsOH treatment). The MDFfibers were first fractionated using p-TsOH at several conditions usinga fiber to acid solution ratio of 1:10. These conditions producedfractionated solids with varying lignin contents, as listed in Table 6.The hydrolyzed solids were thoroughly washed and centrifuged. The washedsamples were dialyzed to separate LCNCs from the partially hydrolyzedLCSR. At neutral pH with conductivity between 1-2 μS/cm, the supernatantthrough centrifugation became turbid, suggesting the presence of LCNCs.The supernatant was then removed and further diluted to 0.01% for AFMimaging. As an example, the thoroughly washed hydrolyzed samples fromP85T80t20, P80T80t20, P65T80t20 were dialyzed. The separated LCNCparticles were fairly well dispersed, as shown by the AFM images inFIGS. 4A, 4B, and 4C. The AFM height measured distributions are shown inFIG. 5 with an average height of 26, 28, and 51 nm, respectively. Thebimodal distribution of sample P85T80t20 was due to the free ligninnanoparticles as shown in FIG. 4A. The AFM images (FIGS. 4A-4C) showedvery interesting morphology of the LCNCs with very long lengths of over1 μm. The great height and long length indicated that the resultantmaterial was CNC bundles.

Example 8: Production of Lignocellulosic Nanofibrils from Birch Wood

The LCSR, after separating LCNCs from the washed hydrolyzed WIS, wassubsequently mechanically fibrillated to produce LCNFs or LCMFs,depending on the extent of fibrillation and the severity of acidhydrolysis. Optionally, especially under low-severity hydrolysisconditions for producing long and entangled LCNFs, LCNCs yield was lowand the washed solids could be directly used for LCNF production withoutdialysis and separating LCNCs. The LCSR, or washed hydrolyzed WISwithout separating LCNCs, was diluted with water to 1% suspensions andfibrillated using a microfluidizer (M-110EH, Microfluidics Corp.,Westwood, Mass.). The suspensions were initially processed through a 200μm chamber 3 times at 40 MPa, and then passed an additional 1-9 timesthrough an 87 μm chamber at 120 MPa. Gelation was observed, suggestingthat the solid suspensions became nanofibrils. Atomic Force Microscopy(AFM) images confirmed this as shown in FIGS. 6A, 6B, and 6C. Thesesamples were produced using LCSR from P50T80t20, P65T80t20, andP80T80t20 after 5 passes through the 87 μm chamber, respectively. AFMmeasured fibril height probability density distributions from thesethree samples are shown in FIG. 7. The corresponding average heights ofthese three LCNF samples were 51.1, 29.4, 15.3 nm. All three LCNFsamples showed remarkable uniformity in height as indicated by thenarrow distributions (FIG. 7). The LCNF with the highest lignin contentcontained lignin nanoparticles (LNPs) clearly visible from the AFM image(FIG. 6). Increased fractionation severity clearly reduced lignincontent (Table 6) and resulted in finer fibrils through mechanicalfibrillation.

Increasing the extent of fibrillation also resulted in LCNFs withthinner diameters and less entanglement. The LCSR from the lowestseverity run P50T80t20 was fibrillated using different passes. AFMmeasured fibril height distributions clearly showed the thinning of thefibril with more passes (FIGS. 8A, 8B, 8C, 8D, and 8E). The mean LCNFheight was reduced from 70 to, 65.2, 51.1, 22.5, 14.3 nm afterincreasing the numbers of passes through the 87 μm chamber of themicrofluidizer from 1 to, 3, 5, 7, and 9 (FIG. 9), respectively.Furthermore, the LCNFs became more uniform with more fibrillation.

Example 9: Production of Lignocellulosic Nanofibrils from Ponderosa Pine

Ponderosa pine, a softwood, was also used to produce LCNFs. Ponderosapine MDF fibers were produced with chips from Yreka, Calif. using thesame 12″ pressurized disk refiner and under the same conditions asdescribed in Example 6. The MDF fibers were then treated using a p-TSOHsolution of 80 wt % concentration at 80° C. for 20 min, or P80T80t20.The acid hydrolyzed sample was washed and 100 g in an oven dry (OD) baseof the washed sample was processed in a Supermasscolloider (Model:MKZA6-2, Disk Model: MKGA6-80#, Masuko Sangyo Co., Ltd, Japan). Themilling consistency was 2%, and the time was 60 min in theSupermasscollioder (SMC). As shown in FIG. 10, whisker-like cellulosenanofibrils were obtained. Unlike microfluidization, however, SMCproduced a non-uniform cellulose nanofibril distribution, as indicatedby the presence of the long fibrils shown in FIGS. 10A and 10B. However,when the SMC samples were subjected to two passes of microfluidization,all particles became very short whisker-like material as shown in FIG.11.

Example 10: Production of Lignin Nanoparticles from Spent Liquor

The results in Tables 1 and 2 demonstrated that a substantial amount ofwood lignin was solubilized, especially for poplar NE222 (hardwood). Itwas found that the solubilized lignin could be precipitated afterdiluting the aqueous spent liquor with additional water because p-TsOHis a hydrotrope. The critical acid concentration at which ligninprecipitation occurred was monitored by dynamic light scattering (DLS)using a zeta potential analyzer (Nanobrook Omni, Brookhaven Instruments,Holtsville, N.Y.). The results from precipitating spent liquor of poplarNE222 at P75T80t20 are presented here. The DLS measured effective ligninparticle sizes in the spent liquor at different dilution ratios, orequivalently the p-TsOH concentrations, are shown in FIG. 12. Theresults show that lignin precipitation was minimal at p-TsOHconcentration ≥15%, as indicated by the very small measured particlesize of less than 300 nm, as well as the minimal increase in size withdilution from the initial high concentration. The measured particle sizerapidly increased to approximately 3000 nm when the spent liquor wasdiluted to a 10% concentration. The increase in particle size was notsubstantial with further dilution to below 4% concentration.

The spent liquor samples at the different dilution ratios werecentrifuged at 3000 g for 10 min. Lignin precipitation was minimal atp-TsOH concentration of 20 wt % and higher. Precipitation increasedsubstantially with dilution and the supernatant changed from highlyopaque to clear. Therefore, the solubilized lignin could be readilyrecovered simply through dilution with water. The lignin recovery yieldvaried with dilution ratio. These results indicate that near fullrecovery can be achieved at p-TsOH concentration of approximately 4%.

Early studies on hydrotropes (Balasubramanian et al. 1989; Hatzopouloset al. 2011) indicated the existence of a minimal hydrotropeconcentration (MHC), also called critical aggregate concentration (CAC),where hydrotropy is exhibited, i.e., below MHC lignin solubilitydisappears. Conductivity measurements were used for estimating the MHC.As shown in FIG. 13, the transition point in the measured conductivityof the diluted p-TsOH aqueous solution was at 11.5 wt %, suggesting MHCor CAC=11.5 wt %. This means that when the concentrated p-TsOH solutionwas diluted below 11.5 wt %, self-association disappeared. Thesolubility of lignin in the solution was impaired, resulting inprecipitation.

Example 11: Characterization of Lignin Nanoparticle Size

The spent liquor at 40 wt % from dissolving poplar wood at P75T80t20 wasdiluted to 10 wt %, below the p-TsOH minimal hydrotrope concentration of11.5 wt %. 10 mL of the diluted spent liquor was centrifuged at 3000 gfor 10 min to precipitate the dissolved lignin. 7.5 mL of DI water wasadded back to further dilute the spent liquor top-TsOH concentration ofapproximately 2 wt %. Almost all dissolved lignin was precipitatedthrough centrifugation. This was due to the strong ionic strength, whichcompressed the double electric layer on the surface of suspended ligninparticles, making the lignin particles aggregate to precipitate outunder the centrifugation force. Most of the ions were removed throughfurther centrifugation and removing supernatant (or acid) followed bydilution, which resulted in a suspension with a p-TsOH concentration of0.4 wt %, centrifugation with 3000 g for 10 min was unable toprecipitate the charge particles due to the strong electrostaticrepulsions among them, resulting in a turbid supernatant. This turbidsupernatant exhibited a significant Tyndall effect; i.e., a red laserbeam was visible in the direction perpendicular to its incidentdirection due to light scattering of very small particles. This showedthat the dispersion was an aqueous sol, or colloidal system, thatcontained nanoparticles of lignin or LNPs.

The turbid supernatant and precipitate after the third centrifuge stepwere thoroughly mixed back together to examine all the lignin particlesin the diluted spent liquor. An AFM topographic image of the resultantwhole diluted suspension deposited on a fresh mica sheet is shown in theFIG. 14. The image confirmed nanoscale lignin particles formed throughself-assembly of dissolved lignin after dilution. The sizes of thelignin nanoparticles ranged from 100 nm to 1 micrometer. Aggregatescould be observed as shown by the multiple peaks in profile 1 in FIG. 15corresponding to line 1 in FIG. 14. Less aggregated particles areobserved from AFM height scanning profiles indicated by the separatedsingle peaks in profile 2 (dashed line in FIG. 15), which correspond toline 2 in FIG. 14; and the diameter and thickness were determined to beapproximately 500 and 50 nm, respectively. This suggests that theresultant LNPs were oblate spheroids.

The mixed diluted spent liquor was centrifuged at different speeds,after which the turbid supernatant was examined by AFM. Larger particleswere precipitated during centrifugation, while only smaller particlesremained in the supernatant. After air drying the supernatant on a micaplate, the sample obtained from centrifugation at 3000 g for 10 mincontained lignin particle aggregates with lateral size of approximately600 nm, as shown in FIG. 16A. Increasing centrifuge speed to 10000 g orhigher, removed additional aggregates and large particles, resulting inrelatively uniform and small LNPs in the supernatant as shown in FIGS.16B and 16C. Typical LNP lateral sizes are approximately 200 and 50 nmat 10000 g and 15000 g, respectively. These results indicate that thediluted spent acid liquor contained lignin particles from tens ofnanometers to approximately 1 micron. Furthermore, the large particlescan be separated through centrifugation. AFM height measurements of thethree supernatant samples are presented in FIG. 17. The heights are muchsmaller than their lateral dimensions. This shows that the LNPs wereoblate spheroid nanoparticles with aspect-ratios (lateral ordiameter:heights or thickness) of approximately 20, based on the resultspresented in FIGS. 16 and 17.

Example 12: Control of Lignin Nanoparticle Size and Surface Charge

Particle charge is a critical property to particle dispersion andcolloidal characteristics. The spent liquor from P75T80t20 at 40 wt %was quickly diluted to 10 wt % and then dialyzed to approximately pH4.5. The average zeta-potential of the LNPs in the dialyzed sample wasapproximately −30 mV. Centrifugation can remove large particles in asuspension resulting in a supernatant that contains smaller particles,as discussed previously. This is clearly shown in FIG. 18 as measured byDLS of the LNPs in the diluted spent acid liquor. Removing largeparticles may also have facilitated particle dispersion in water, sincethe zeta potential increases from approximately −30 mV to −45 mV for theremaining LNPs in the supernatant after removing large particles usingcentrifugation at 3000 g (or higher) for 10 min (FIG. 18).

The speed of dilution was found to affect LNP morphology. 5 g of thespent liquor at a p-TsOH concentration of 40% from the run P75T80t20 wasmixed with 15 g DI water using a peristaltic pump at four different flowrates of 0.19, 0.95, 2.85 and 5.71 mL/min, respectively. The dilutionspeed was determined in terms of dilution times/min. An extremely fastdilution speed of 240 times/min was achieved by manually adding 15 g ofwater into the flask in 1 second. A final dilution ratio of 4 times wasapplied in all dilution experiments to p-TsOH concentration of 10 wt %.The dissolved lignin aggregates when the spent liquor is diluted to 10wt % (below the MHC of 11.5 wt %). The speed of dilution or water mixingwith the hydrotropep-TsOH during dilution affected lignin aggregationand dispersion. DLS measured LNP size decreased rapidly fromapproximately 900 nm, when the spent acid liquor was diluted to 10 wt %at the slowest rate, to 450 nm when diluted at the fastest rate, asshown in FIG. 19A. The DLS measured particle sizes were alsoqualitatively in agreement with the lateral diameters from AFM images(FIGS. 20A, 20B, and 20C). The increase in particle size was a directresult of dissolved lignin aggregation during dilution. Apparently, aslow dilution increased the dissolved lignin aggregation time andresulted in a larger DLS particle size than that obtained via a fastdilution. A longer aggregation time also resulted in the increase in thethickness of lignin aggregates, as confirmed by the AFM measured heightdistributions (FIG. 19B).

For negatively charged LNPs, pH and ionic strength can affect theiraggregation and charge. The effects of pH were investigated by spiking asolution of NaOH at 0.1 mol/L or with HCl at 0.1 mol/L into the ligninsupernatant from centrifuging at 3000 g for 10 min and subsequentlydialyzing to pH 4.5. DLS measured LNP mean particle sizes wererelatively stable between pH 3.0-10 with a slight reduction in size aspH increased to approximately 7.5, followed by a slight size increase asthe pH increased to 10, as shown in FIG. 21A. Reducing pH below 3 orincreasing pH above 10 resulted in a rapid increase in DLS measured LNPsize. This was also verified by AFM imaging as shown in FIGS. 22A, 22B,and 22C. The results shown in FIG. 21A show that pH is a good parameterto control LNP size. Furthermore, within a wide range of pH 3-10, meanDLS LNP size was fairly constant. This is important for LNPapplications.

Zeta potential shows the opposite trend of LNP size with respect to pH.With increasing pH, the zeta potential increased (absolute value)rapidly from about −4 mV to approximately −50 mV at about pH 8, and thendecreased rapidly as the pH rose to near 12. The maximal zeta potentialcorresponded closely to the smallest LNP size (FIG. 21A), showing thatelectrostatic repulsion played a major role in lignin particleaggregation. The results also indicated that a zeta potential of −25 mVor higher (absolute value) was desirable to avoid substantial ligninparticle aggregation, as shown by the rapid increase in LNP size at zetapotential below 25 mV.

The result of the dilution experiments showed that ionic strengthaffected colloidal suspension precipitation behavior by affecting thedouble electric layer surrounding the LNP surface. The effect of ionicstrength on LNP size was evaluated by spiking a NaCl solution into adialyzed LNP suspension of pH 6.4. As the concentration of NaCl wasincreased to 20 mM, the zeta-potential of the LNP was decreased (inabsolute value) from approximately −50 mV to −25 mV, at which pointthere was a rapid increase in particle size due to aggregation, as shownin FIG. 23A. This critical zeta-potential of −25 mV is in agreement withthat observed in the pH effect study (FIG. 21A). The aggregationphenomenon is clearly shown by AFM imaging, as shown in FIGS. 24A, 24B,and 24C as well as AFM measured height distributions (FIG. 23B).

Fractionation conditions also affected the LNP size. As listed in Table7, more severe reaction conditions resulted in a larger LNP particlesize for both NE222 and Douglas-fir. In addition, more severe reactionconditions often resulted in increased dissolution of lignin. The amountof lignin dissolved and DLS measured LNP size were correlated as shownin FIG. 25 (NE222). More lignin dissolution resulted in a higher LNPconcentration in the diluted spent liquor at 10 wt %. A higher ligninconcentration certainly could have increased aggregation, simply due tothe increased collision probability among lignin particles. The amountof lignin dissolved in a spent liquor was determined from the ligninmass balance by evaluating the residual lignin in the washed waterinsoluble solids. As a verification, the amount of dissolved lignin wasalso determined by diluting the spent liquor to 4% to fully precipitatedissolved lignin. The precipitated lignin was then washed thoroughly.The oven dry weight of the washed lignin was measured gravimetricallyfor yield determination (listed in Table 7). Discrepancies existedbetween these two methods (Table 7), perhaps due to losses inprecipitation and washing.

TABLE 7 Lignin nanoparticles from different treatment of poplar andDouglas fir measured from the spent acid solution diluted to 10%.Biomass Treatment Lignin dissolved (%) Diameter Zeta Potential SpeciesCondition Solid Liquor nm mV NE222 P70T50t20 29.8 25.0 349.7 ± 1.5 −40.0± 0.2 P70T65t20 65.1 63.9 371.7 ± 8.4 −36.5 ± 0.2 P70T65t35 63.9 60.3413.7 ± 2.1 −41.4 ± 1.0 P70T80t20 77.6 68.2 441.5 ± 4.2 −35.1 ± 0.3P75T65t20 71.6 63.9 438.6 ± 5.1 −33.8 ± 0.7 P75T65t35 77.4 60.7 474.8 ±3.2 −41.1 ± 1.2 P75T65t60 81.0 58.7 500.4 ± 1.6 −36.7 ± 2.2 P75T80t2085.5 73.7 467.1 ± 2.5 −37.9 ± 3.6 P80T80t20 90.7 78.6 529.6 ± 7.4 −34.1± 1.3 Fir P70T80t20 26.5 25.0 518.5 ± 4.6 −36.7 ± 0.9 P75T80t20 36.326.1  605.3 ± 17.9 −35.2 ± 0.7 P80T80t20 53.9 52.6  888.4 ± 122.7 −32.9± 0.5

Table 7 also indicates that LNPs from softwood have a much larger sizethan that from poplar NE222. All LNPs from different fractionationconditions have very high negative zeta potential as listed in Table 7,indicating that all LNPs could be well dispersed in liquids.

Example 13: Lignin Nanoparticle Size Stability

Colloidal stability of LNPs is important for a variety of applications.The diluted p-TsOH spent liquor from P75T80t20 at 40 wt % was used tostudy LNP colloidal stability. The spent liquor was further diluted to10 wt %, then dialyzed to a pH of approximately 4.5. The dialyzed LNPsuspension was then centrifuged at 3000 g for 10 min. The precipitatedlignin from centrifugation was re-suspended in DI water. The stabilitiesof the LNPs in the supernatant from the centrifuge and in the suspensionof re-suspended precipitates were analyzed periodically using dynamiclight scattering (DLS) for a period of two weeks. Samples of eachsuspension was first vigorously hand shaken each time before DLSanalyses. AFM images of each suspension at time zero and at the end oftwo weeks were also taken. DLS analyses show that the DLS size of theLNPs in the supernatant was slightly increased gradually during a periodof two weeks from approximately 310 nm to 370 nm (FIG. 26). Over thesame period, mean zeta-potential gradually decreased from −28 mV to −11mV (FIG. 27). AFM images obtained at time 0 and after two weeksconfirmed the increase in LNP size (FIGS. 28A and 28B). The increase inLNP size was a direct result of particle aggregation. This aggregationalso increased the particle thickness as shown by the AFM measuredparticle height probability density (FIG. 29).

DLS-measured mean size of LNPs in the suspension of the re-suspendedprecipitated lignin decreased over a period of two weeks from 540 nm to450 nm (FIG. 26). The resuspension of these precipitated particles in DIwater increased the pH of the suspension, which resulted in a highsurface charge (FIG. 27), according to the results shown in FIGS. 21Aand 21B, and prevented aggregation during drying for AFM imaging. TheAFM-measured particle thickness measurements (FIG. 31) werequalitatively in agreement with the DLS size measurements. FIG. 30A isan AFM image of LNPs from a suspension of re-suspended precipitates.FIG. 30B is an AFM image of LNPs in a supernatant from a centrifuge att=0.

Example 14: p-TsOH-Based Delignification for Wood Fiber Production UsingBirch Wood

The birch MDF described in Example 6 was used to produce corrugatedmedium fibers through p-TsOH-based lignocellulosic biomassfractionation. Most of the data listed in Table 8 were obtained fromExample 6, but are presented in terms of component yields in theoreticalpercentages as compared to mass-based component yields in Table 6.Different degrees of delignification could be achieved by varyingreaction severity. The scale-up run T50P81t27, using 750 g in oven dry(OD) weight MDF, resulted in similar results as the lab scale runT50P80t20. The scale-up run had slightly increased delignification dueto a slightly longer reaction time of 27 min (including a 0.5*heat-upperiod of 14 min).

TABLE 8 Chemical compositions of p-TsOH fractionated birch MDF samplesunder different conditions. The numbers in the parentheses are componentrecovery yields theoretical percentages. Solids yield Glucan XylanMannan Lignin Sample Label¹ (%) (%) (%) (%) (%) Untreated Birch 36.222.5 1.2 22.5 Birch MDF 100.0 34.6 20.8 1.9 23.0 P40T80t55 60.6 51.7(90.5) 13.3 (38.8) 2.3 (73.7) 17.6 (46.4) P50T80t20 56.7 59.2 (97.0)15.0 (40.8) 2.4 (70.8) 16.0 (39.3) P50T80t40 59.6 53.7 (92.4) 13.0(37.3) 2.0 (63.5) 15.3 (39.5) P50T80t80 56.5 61.1 (99.8) 11.9 (30.9) 2.4(72.5) 13.8 (34.0) P65T80t20 54.2 62.0 (97.0) 14.0 (36.4) 2.6 (74.9)11.6 (27.4) P80T80t20 51.3  67.7 (100.4) 12.2 (30.0) 2.5 (68.2)  7.2(16.0) P50T81t27² 52.8 57.7 (89.8) 14.7 (36.7) 2.7 (74.6) 15.1 (35.4)¹(Pxx, Txx, txx) stands for p-TsOH concentration in wt %, reactiontemperature in ° C. and reaction duration in min. ²scale-up run at 750g, average temperature.

Based on the amount of lignin removal from the lab bench scale run, atargeted reaction condition of P50T80t20 was chosen for a scale-up studyto produce corrugated medium fibers. The actual reaction conditionP50T81t27 deviated slightly due to difficulties in controlling the exacttemperature using steam-jacket heating and the increased heat-up periodof the larger scale-up reactor. The lignin content of the p-TsOH-basedfractionation of the fibers was 15% (Table 8) after solubilizing 65% ofthe wood lignin. This lignin content is about the same as that oftypical corrugated medium pulp fibers. The morphologies of thedelignified fibers are shown in FIG. 32B in comparison with the initialMDF fibers in FIG. 32A. Typical MDF fibers have a length over 2 mm, duemainly to the presence of many fiber bundles. The p-TsOH treatmentseparated the fiber bundles. The length of these separated fibers wasover 1 mm. Refining reduced fiber length, but improved fiberfibrillation, as can be seen from the optical and scanning electronicmicroscopic (SEM) images (FIGS. 33A and 33B).

Due to difficulties in making high basis weight sheets in thelaboratory, the initial studies on the mechanical properties are fromsheets with basis weight of 60 g·m⁻². The results indicate that atensile index of approximately 25 N·m·g⁻¹ was achieved after refining toapproximately 500 (mL) Canadian Standard Freeness (CSF) (FIG. 34A). Thefailure strain is shown in FIG. 34B.

Example 15: p-TsOH-Based Fractionation of an Agricultural Residue: WheatStraw

Lightly hammer-milled wheat straw was fractionated directly usingconcentrated p-TsOH solution in a range of conditions similar to thatdescribed in Example 1. The wheat straw was first water washed to removedirt. Good selectivity in dissolving lignin over cellulose was obtained,as listed in Table 9. At a relatively low p-TsOH acid concentration of40 w %, over 50% straw lignin dissolved while over 85% of cellulose wasretained. Wheat straw usually contains a substantial amount of silicate,as can be seen from the high ash content of 5.1% listed in Table 9(obtained by burning at 560° C. the residual solids after a two-stepsulfuric acid hydrolysis of carbohydrates). It appears that silicate wasfully retained in the WIS after p-TsOH-based lignocellulosic biomassfractionation. This is beneficial, as it helps to increase the WIS yieldfor material production as well as avoiding silicate-caused equipmentcorrosion problems in downstream processing. The silicate can alsoimprove the hydrophobicity of the solids for LCNF or LCMF production.

TABLE 9 Chemical compositions of p-TsOH-based fractionation of wheatstraw samples under different conditions. The numbers in the parenthesesare component yields based on the component in the untreated wheatstraw. Solids Sample yield Glucan Xylan Ash K. Lignin Label ¹ (%) (%)(%) (%) (%) Untreated 100 40.8 24.5 5.1 20.4 Wheat Straw P20T40t20 94.741.4 (95.9) 22.9 (88.3) 5.3 (97.7)  20.7 (96.2) P20T50t20 93.3 39.5(90.2) 21.8 (82.8) 5.5 (100.4) 19.9 (91.2) P20T60t20 89.8 38.3 (84.2)21.5 (78.5) 6.4 (111.9) 19.5 (85.9) P25T60t30 87.3 41.1 (88.0) 22.0(78.3) 5.2 (87.7)  19.0 (81.7) P25T60t30R 87.3 41.7 (89.2) 22.9 (81.4)6.1 (103.6) 19.8 (85.1) P35T60t30 80.5 43.2 (85.2) 20.5 (67.4) 8.2(128.1) 20.7 (81.8) P35T60t60 75.5 45.4 (84.0) 17.9 (55.2) 7.1 (104.2)19.1 (70.7) P40T70t60 67.1 48.3 (79.4) 14.9 (40.7) 9.0 (117.4) 17.8(58.5) P40T80t60 66.0 54.7 (88.6) 13.4 (36.1) 8.9 (114.1) 16.9 (54.8)P40T80t60R 66.0 52.5 (84.9) 13.3 (35.9) 7.6 (97.2)  17.2 (55.8)P40T80t90 58.3 57.7 (80.4) 12.0 (27.9) 9.2 (104.0) 16.3 (46.8)P40T80t120 62.3 56.3 (88.1) 11.7 (30.5) 9.2 (111.8) 15.8 (48.4)P50T80t60 57.2 55.1 (77.1) 11.4 (26.5) 9.5 (105.5) 14.4 (40.5) P50T80t9056.0 59.0 (80.9) 10.9 (24.9) 9.2 (99.8)  14.0 (38.6) P60T80t60 55.0 62.1(83.8) 10.0 (22.4) 8.5 (91.2)  11.2 (30.3) P60T80t90 55.0 59.3 (79.9) 8.5 (19.1) 10.1 (108.4)  14.0 (37.9) ¹ (Pxx, Txx, txx) stands forp-TsOH concentration in wt %, reaction temperature in ° C. and reactionduration in min. R stands for replicate fractionation run. R stands forreplicate fractionation run.

Example 16: p-TsOH-Based Fractionation of an Energy Crop: Switchgrass

Mildly hammer-milled switchgrass was also fractionated usingconcentrated p-TsOH solution in the range of conditions used for thewheat straw in Example 14. The switchgrass was also washed and air driedbefore use. Again, good selectivity of dissolved lignin over cellulosewas achieved. The relatively lower dissolution of lignin ofapproximately 60% compared to 85% for wood described previously wasperhaps due to the relatively larger size of the materials as well asthe relatively low p-TsOH concentrations used in the p-TsOH-basedfractionation. Further hammer-milling the switchgrass is expected toachieve improved dissolution of lignin.

TABLE 10 Chemical compositions of p-TsOH-based fractionation ofswitchgrass samples under different conditions. The numbers in theparentheses are component yields based on the component in the untreatedswitchgrass. Solids yield Glucan Xylan K. Lignin Sample Label ¹ (%) (%)(%) (%) Untreated 100 37.3 26.1 23.5 Switchgrass P20T40t20 91.4 40.1(98.2) 25.2 (88.5) 23.0 (89.5) P20T50t20 90.2 39.6 (95.7) 26.5 (91.6)23.7 (91.0) P20T60t20 89.6 40.3 (96.9) 25.5 (87.6) 24.4 (93.2) P25T60t3087.8 39.4 (92.7) 26.4 (88.9) 24.2 (90.5) P25T60t30R 87.8 40.7 (95.8)25.6 (86.2) 23.1 (86.4) P35T60t30 83.4 41.7 (93.2) 25.4 (81.1) 24.8(87.9) P35T60t60 76.4 42.3 (86.6) 20.7 (60.7) 24.9 (81.2) P40T70t60 68.251.7 (94.5) 19.8 (51.8) 23.9 (69.4) P40T80t60 59.7 52.5 (83.9) 14.5(33.2) 22.7 (57.6) P40T80t90 59.4 48.8 (94.4) 13.2 (30.0) 21.3 (53.9)P40T80t120 59.3 59.2 (78.6) 12.5 (28.4) 19.9 (50.3) P50T80t60 57.4 49.4(88.5) 13.5 (29.8) 20.7 (50.5) P50T80t90 55.1 57.5 (86.9) 13.5 (28.4)19.0 (44.6) P60T80t60 55.1 58.9 (93.2) 12.0 (25.4) 19.6 (45.9) P60T80t9052.9 63.1 (92.3) 11.1 (22.5) 18.7 (42.1) ¹ (Pxx, Txx, txx) stands forp-TsOH concentration in wt %, reaction temperature in ° C. and reactionduration in min. R stands for replicate fractionation run. R stands forreplication fractionation runs.

Example 17: Solubilization of Commercial Technical Lignin Using anAqueous p-TsOH Solution

Commercial lignin is readily available but cannot be solubilized inaqueous systems to produce micro or nanoparticles. Aqueous p-TsOH wasalso used to solubilize commercial alkali technical lignin purchasedfrom Sigma-Aldrich (St. Louis, Mo.). At a given temperature of 80° C.,alkali lignin was gradually added into a 100 g of p-TsOH solution withstirring until the solution could no longer solubilize lignin, asobserved from precipitation. The solubility was the maximal amount oflignin solubilized in the 100 g solution. As shown in FIG. 35A, ligninsolubility at 80° C. was increased with p-TsOH concentration. Solubilityincreased rapidly at p-TsOH concentrations above 40 wt %, with asolubility of 35 g/100 g at a p-TsOH concentration of 55 wt %. Ligninsolubility was also increased with temperature, as shown in FIG. 35B,and reached a plateau at approximately 65° C. at a p-TsOH concentrationof 50 wt %. The solubilized lignin was separated through centrifugationafter diluting the solution to 10 wt % with water to precipitate lignin.AFM images revealed that the precipitated LNPs had a circular shape witha lateral diameter of approximately 100-200 nm, as shown in FIGS. 36A,36B, and 36C. The AFM topographic measured heights indicated averageheights were approximately 4-6 nm, as shown in FIG. 37. Gel permeationchromatography (GPC) molecular measurements indicated that Mw wasapproximately 7000, as listed in Table 11, except for the run at asevere condition of P55T80.

TABLE 11 GPC measured molecular weight of LNPs from solubilizing alkalilignin in p-TsOH solutions Run Mn Mw PDI P40T35 1791 7480 4.18 P40T651812 7098 3.91 P50T65 1774 7282 4.10 P55T80 2130 11934 5.60

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The word “illustrative” is used herein to mean serving as an example,instance, or illustration. Any aspect or design described herein as“illustrative” is not necessarily to be construed as preferred oradvantageous over other aspects or designs. Further, for the purposes ofthis disclosure and unless otherwise specified, “a” or “an” means “oneor more.”

The foregoing description of illustrative embodiments of the inventionhas been presented for purposes of illustration and of description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed, and modifications and variations are possible inlight of the above teachings or may be acquired from practice of theinvention. The embodiments were chosen and described in order to explainthe principles of the invention and as practical applications of theinvention to enable one skilled in the art to utilize the invention invarious embodiments and with various modifications as suited to theparticular use contemplated. It is intended that the scope of theinvention be defined by the claims appended hereto and theirequivalents.

What is claimed is:
 1. A method for treating lignocellulosic biomass,the method comprising: dispersing a lignocellulosic biomass in anaqueous solution comprising a hydrotropic solid organic acid, whereinthe concentration of the hydrotropic solid organic acid in the solutionis higher than its minimal hydrotrope concentration; maintaining thesolution at a temperature and for a time sufficient to dissolve at least10 wt. % of the lignin in the lignocellulosic biomass; and separatingthe solution and the dispersed lignocellulosic biomass into a spent acidsolution comprising dissolved lignin and a water-insolublecellulose-rich solids fraction comprising water-insolublelignocellulosic solid residues.
 2. The method of claim 1, wherein thetemperature is no greater than 100° C. and the time is no greater than300 minutes.
 3. The method of claim 1, wherein the lignocellulosicbiomass comprises wood chips, milled wood, commercial technical lignin,or a combination thereof.
 4. The method of claim 1, wherein thelignocellulosic biomass is a hardwood and at least 10 wt. % of thelignin in the hardwood is dissolved.
 5. The method of claim 1, whereinthe lignocellulosic biomass is softwood and at least 10 wt. % of thelignin in the softwood is dissolved.
 6. The method of claim 1, whereinthe lignocellulosic biomass is commercial technical lignin and theamount of the technical lignin dissolved is at least 2 g/100 g solution.7. The method of claim 1, further comprising fibrillating thelignocellulosic biomass prior to dispersing the lignocellulosic biomassin the aqueous solution comprising the hydrotropic solid organic acid.8. The method of claim 1, further comprising precipitating ligninnanoparticles from the spent acid solution.
 9. The method of claim 1,further comprising converting sugars dissolved in the spent acidsolution into furans and separating the furans from the spent acidsolution.
 10. The method of claim 1, further comprising mechanicallyfibrillating the lignocellulosic solid residues to form lignocellulosicmicrofibrils, lignocellulosic nanofibrils, or a combination thereof. 11.The method of claim 10, wherein the water-insoluble cellulose-richsolids fraction comprises lignocellulosic solid residues andlignocellulosic nanocrystals.
 12. The method of claim 10, furthercomprising separating the lignocellulosic solid residues from thelignocellulosic nanocrystals.
 13. The method of claim 1, furthercomprising converting the water-insoluble lignocellulosic solid residuesinto sugars via hydrolysis using enzymes or chemicals.
 14. The method ofclaim 1, further comprising recycling the hydrotropic solid organic acidin the spent acid solution back into the aqueous solution comprising thedispersed lignocellulosic biomass.